Method of anesthesia

ABSTRACT

The method of inducing anesthesia by administering an anesthetically effective amount of the compound fluoromethyl 1,1,1,3,3,3-hexafluoro-2-propyl ether.

United States Patent 15] 3,683,092 Regan et al. 1451 Aug. 8, 1972 [54] METHOD OF ANESTHESIA [72] Inventors: Bernard M. Regan; John C. Long- [56] References Cited street, both of Chicago, Ill. UNITED STATES PATENTS [73] Assgnee f 3,476,860 11/1969 Croix et a1 ..424 342 [22] F1 d J l 31 l'970 3,527,814 9/1970 Croix etal ..424/342 1e uy 21 L 0 130 Primary Examiner-Jerome D. Goldberg Attorney-Scott J. Meyer Related US. Application Data [63] Continuation-impart of Ser. No. 771,365, Oct. [57] ABSTRACT 28, 1968, abandoned. The method of inducing anesthesia by administering an anesthetically effective amount of the compound 8| fluommethy] 1,1,1,33,3 hexafluoro z propyl ether 11 [58] Field of Search ..424/342; 260/614 F. 3 Claims, No Drawings METHOD OF ANEsnnsrA CROSS-REFERENCE TO RELATED APPLICATION This is a continuation-in-part of co-pending application Ser. No. 771,365, filed Oct. 28, 1968 now abandoned.

This invention relates to the fluorinated ether, fluoromethyl l l 1 ,3 ,3 ,3-hexafluoro-2-propyl ether, having the structure CH F-O-CH(CF;,

In recent years, several fluorinated ethers have been found to have useful anesthetic properties, notably methoxyflurane, CH OCF CHCI fluroxene, CF CH OCH CH roflurane, CH OCF CI-[BrF; and ethrane, CHF OCF CHClF.

With the recent availability of various polyhalo isopropanols, which serve as excellent starting materials for the corresponding methyl ethers, certain anesthetic halogenated isopropyl methyl ethers have been developed. U.S. Pat. No. 3,476,860 describes a group of halogenated derivatives of fluorinated isopropyl methyl ethers of which two compounds, namely, CF (CF Cl)CHOCl-I Cl and (CF Cl-lOCI-l Cl, were stated to be anesthetic. That patent also describes the preparation of several other related compounds, for example, (CF CHOCl-IF and (CF CH OCHFCl.

Surprisingly and unexpectedly, it has now been found that the present fluoromethyl l,l,l,3,3,3-hexafluoro-2-propyl ether, which was not mentioned in U.S. Pat. No. 3,476,860, is an outstanding anesthetic agent. On the other hand, the foregoing two specific compounds suggested as anesthetic agents in said patent, and several of the other related compounds described in said patent, have now been found upon further testing to have undesirable properties which mitigate against their use as clinically useful anesthetics.

That is, it has now been found that when administered to dogs in repeated doses for long periods of time, the compounds having a chlorinated methyl group, for example, (CF CHOCH Cl, are unstable and toxic to the animal, while that compound having a difluorinated methyl group, for example, (CF CH OCHF is convulsant. The monochlorinated compound, (CF CHOCHFCI, also produces opisthotonus in mice. On the other hand, the present fluoromethyl 1,1,l,3,3,3-hexafluoro-2-propyl ether exhibits outstanding anesthetic properties over repeated and long term dosage administration in dogs. Consequently, the present compound has an unexpected and unobvious utility not exhibited by those compounds mentioned in U.S. Pat. No. 3,476,860.

Although the present inventors are not to be bound by theory, it is believed that the instability and toxicity of the chlorinated ether, (CF CHOCH C1, is due to the hydrolysis or breakdown of this compound to the reaction products formaldehyde, hydrochloric acid and hexafluoroisopropanol. This toxicity is believed to be due primarily to the formation of the formaldehyde and hydrochloric acid since upon intravenous administration of hexafluoroisopropanol to dogs, the latter compound by itself was not found to be toxic. These reaction products have been found to be formed during long term dosage administration of the anesthetic, (CF CHOCH CI, in an amount of about 170 times the amount that the corresponding reaction products are formed with the present fluoromethyl l,l,l,3,3,3- hexafluoro-Z-propyl ether.

The outstanding utility of the fluoromethyl 1,1,1 ,3,3,3-hexafluoro-2-propyl ether of the present invention is further highlighted by comparison with isomers of that compound which do not have this utility. For example, the compound CH OCF(CF was found to be non-anesthetic up to 8 percent by volume in oxygen, which means that it would burn at its anesthetic concentration since its lower flammability limit is about 7 to 8 percent. Another isomer, the trifluoromethyl 2,2,3,3-tetrafluoropropyl ether of Al dridge and Shepherd, J. Org. Chem, Vol. 29, pages 1 l-l5 (1964), has been shown to cause violent convulsions and deaths in mice at a concentration as low as 0.5 percent. Yet another isomer, CHF OCH CF CF is non-anesthetic up to its lethal concentration and produces convulsions in mice. In still another comparison, it has been found that the isomeric (CHF C FO-CHF is a weak anesthetic in which deep anesthesia is not obtained and abnormal EEG (electroencephalographic) and convulsant activity is observed.

All of the foregoing comparisons between the novel fluorinated ether of this invention and several isomeric ethers further supports the unobvious and unexpected utility of the present invention.

The fluoromethyl l l 1 ,3,3,3-hexafluoro-2-propyl ether of this invention is a volatile liquid, is nonflammable in air at ambient temperatures and has a lower flammability limit in oxygen of about 11.8 volume percent, which is about three times its anesthetic maintenance concentration in dogs.

Fluoromethyl l 1,1,3,3,3-hexafluoro-2-propyl ether is prepared by several methods. In one method, the chloromethyl 1,l,l,3,3,3-hexafluoro-2-propyl ether is first prepared by the free radical chlorination of l,1,l,3,3,3-hexafluoro-2-propyl methyl ether and, more preferably, by a photo induced reaction between about 0.5 to about 1 mole of chlorine per mole of the hexafluoro-Z-propyl methyl ether and a temperature of from about 20 C. to about 65 C. The chlorine is then replaced with fluorine in the methyl group. In this replacement reaction, the chloromethyl ether is reacted with from about 1 to about 3 molar equivalents of dry potassium fluoride in the presence of a mutual solvent, for example, an organic solvent such as tetrahydrothiophene 1,1-dioxide, under essentially anhydrous conditions and a temperature of from about C to about C.

Another method of preparation of the present anesthetic compound involves the reaction of the corresponding methyl ether and bromine trifluoride in accordance with a general procedure disclosed by Yuminov et al., Zh. Obshch. Khim., Vol. 37, pages 375-380 (1967); Chem. Abstracts, Vol. 67, No. 43357x. In this reaction, fluoromethyl l,l,l,3,3,3-hexafluoro-2-propyl ether is prepared from 1,l,l,3,3,3- hexafluoro-2-propyl methyl ether and from about 0.5 to about 1.0 molar equivalent of bromine trifluoride, preferably about two-thirds of a molar equivalent, by refluxing at about 20 C to about 50 C.

Still another method of preparation of the present anesthetic ether involves the reaction of 1,3- polyfluoro-2-propanol, formaldehyde and hydrogen fluoride in accordance with a general procedure described by Weinmayr, U.S. Pat. No. 2,992,276.

Surprisingly and unexpectedly, the compound of the present invention cannot be prepared by the halogen replacement methods described in examples 3 and 4 of U.S. Pat. No. 3,476,860, which involve the reaction of the corresponding chlorinated ether and antimony trifluoride. That is, the fluoromethyl 1,1,1,3,3,3-hexafluoro-2-propyl ether cannot be prepared by the reaction of (CF CHOCH Cl and antimony trifluoride as is taught in said patent for the preparation of the corresponding (CF CI-IOCI-1F and (CF CHOCHFC1.

In general, the anesthetic compound of this invention is administered by the inhalation route to warm blooded, air breathing animals in an amount of from about 1 percent to about 5 percent by volume in admixture with from about 99 percent to about 95 percent by volume of oxygen or a gaseous mixture containing oxygen in sufficient amount to support respiration.

Although specific methods of administration of the fluoromethyl 1,1,1,3,3,3-hexafluoro-2-propyl ether as an anesthetic agent are described herein, it will be understood that this compound is not limited to any particular method of administration. Thus, the fluorinated ether of this invention can be admixed with one or more other anesthetic agents in order to achieve advantages in administration, degree of relaxation, safety and the like. For example, the present compound can be admixed with suitable proportions of known anesthetics such as nitrous oxide, ethyl ether, cyclopropane, halothane, ethyl vinyl ether and the like anesthetic adjuncts. In nitrous oxide, the lower flammability limit of fluoromethyl 1,1,1,3,3,3-hexafluoro2- propyl ether is percent by volume whereas the lower flammability limit of the analagous chloromethyl 1,1,1,3,3,3-hexafluoro-2-propyl ether of U.S. Pat. No. 3,476,860 in nitrous oxide is 6 percent by volume. The significance of this advantage is apparent since the use of nitrous oxide along with oxygen is known to generally have an adverse effect upon the flammability of organic compounds.

The fluorinated ether of this invention can also be injected directly into the body by means of a catheter or shunt [see, e.g., Folkman et al., Science, Vol. 154, pages 148-149 (1966)] or can be prepared in an emulsion form of the oil-in-water type and injected into the animal to evolve satisfactory anesthesia [see, e.g., Krantz et al., Anesth. and Analg., Vol. 41, pages 257-262 (1962 and U.S. Pat. No. 3,216,897]. The anesthetic agent enters the central nervous system via the circulatory blood and leaves the body in the exhaled air in a manner analagous to the inhalation route of administration. Still other methods of administration will be apparent to those skilled in the art.

The following examples will further illustrate the present invention although the invention is not limited to these specific examples. All parts and percentages set forth herein are on a weight basis unless otherwise specified.

EXAMPLE 1 Chloromethyl 1 ,1 1 ,3,3,3-l-Iexafluoro-2-propyl Ether Chlorine gas (165 grams, 2.32 moles) was bubbled into 1 1, l ,3,3,3-hexafluoro-2-propyl methyl ether (420 grams, 2.32 moles) during four hours. After 5 minutes, the reaction was initiated by illumination with a sun lamp through a Pyrex reaction flask for about 5 minutes. Thereafter, the exothermic reaction was allowed to proceed autogeneously under partial reflux (hydrogen chloride emitted) employing a Dry Ice condensor. The reaction product was washed successively with cold water, a small amount of aqueous sodium bisulfite and cold water made slightly alkaline with sodium hydroxide. The washed product weighed 478 grams. It was dried by azeotropic distillation and then fractionally distilled at 747 mm. Hg. A forerun of 79 grams, b 6577.2 C, was first obtained. The next 281 grams, b 77.277.3 C, was chloromethyl l,1,1,3,3,3- hexafluoro-2-propyl ether of 99.8 percent pun'ty by gas liquid chromatography (GLC) and with a density of 23 C of about 1.517. The CH ClO-CH(CF structure was confirmed by a proton nuclear magnetic resonance (NMR) spectrum.

EXAMPLE 2 Chloromethyl 1,1 1 ,3,3,3-Hexafluoro-2-propyl Ether Dry chlorine gas (685 grams, 9.66 moles) was bubbled at an average rate of 31 grams per hour into methyl 1,1,1,3,3,3-hexafiuoro-2-propyl methyl ether (2,712 grams, 14.9 moles) at 20 to 25 C with illumination by an immersion-type water cooled ultraviolet lamp through a Pyrex sleeve. The reaction flask was surmounted by a cold water condensor, and this condensor was surmounted by a Dry Ice cooled condensor connected to a Dry Ice cooled trap which permitted the release of hydrogen chloride. The product was washed with ice cold water, cold dilute aqueous sodium hydroxide solution, and cold water. It was separated, dried by azeotropic distillation, and fractionally distilled to recover 1,1,l,3,3,3-hexafluoro- 2-propyl methyl ether (1,171 grams), h 502 to 510 C, of 99.9 percent purity by GLC. Subsequently, a chloromethyl 1,1,1,3,3,3-hexafluoro-2-propyl ether fraction (1,346 grams), b 77.0 to 772 C, of 99.9 percent purity by GLC was obtained.

EXAMPLE 3 Fluoromethyl 1 l ,1,3,3,3-Hexafluoro-2-propyl Ether A solution of chloromethyl 1,1,1,3,3,3-hexa.fluoro-2- propyl ether (754 grams, 3.49 moles) in dry tetrahydrothiophene 1,1-dioxide (2,000 ml) and dry, powdered potassium fluoride (203 grams, 3.49 moles) were stirred and heated to C in a creased flask fitted with a fractional distillation assembly. A distillate (200 ml), b 560 to 62 C, was collected during 5 hours. Then the reaction mixture was cooled to room temperature, dry potassium fluoride (100 grams, 1.74 moles) was added, and the cycle of operations was repeated three times at temperatures between 138 to to give distillates 100 m1, 100 ml and 50 ml), b-,.,, 58 to 61 C, 555 to 57 C, and 54.2 to 559 C, respectively. From this portionwise addition of potassium fluoride (503 grams total, 8.7 moles) there was obtained distillates totalling 672 grams, b 54.2 to 62.0 C, which by GLC analysis was about 92 percent fluoromethyl and 6.8 percent chloromethyl 1,1, l ,3,3 ,3- hexafluoro-Z-propyl ethers. The combined distillates were dried over anhydrous calcium sulfate (33 grams) and filtered.

Fractional distillation of 659 grams gave a forerun (46 grams), b 535 to 57.0 C, and then 99.6 percent pure fluoromethyl 1 1 1 ,3,3,3-hexafluoro-2-propyl ether (505 grams), b 570 to 57.7 C. There remained 94 grams of undistilled substance.

The fluoromethyl ether fraction (311 grams), b

EXAMPLE 4 Fluoromethyl 1 l 1 ,3 ,3 ,3-Hexafluoro-2-propyl Ether Bromine trifluoride (14.5 ml, 0.34 mole) was added portionwise during two hours to 1,1,1,3,3,3-hexafluoro-Z-propyl methyl ether (45 ml, 0.34 mole) with stirring in a Pyrex flask fitted with a reflux condenser and a Teflon syringe and needle. A vigorous exothermic reaction occurred at about 20 C and higher. The reaction temperature was maintained between 20 and 50 C with the aid of a water bath. A proton NMR spectrum of the product indicated the conversion of the methyl ether to the corresponding fluoromethyl ether was substantially complete. The product was washed with aqueous sodium sulfite, aqueous sodium hydroxide, and water to decolorize and neutralize. The washed product (61 grams) was dried over anhydrous calcium chloride and shown by GLC analysis to be 97.5 percent fluoromethyl 1 ,1 l ,3,3,3-hexafluoro-2-propyl ether.

EXAMPLE 5 Fluoromethyl l 1 1 ,3,3 ,3-Hexafluoro-2-propyl Ether 1,1,1,3,3,3-hexafluoro-2-propyl methyl ether (622 grams, 3.41 moles) was stirred in a reactor fitted with an additional funnel containing bromine trifluoride (301 grams, 2.20 moles) and a cold water condenser connected to an ice-cooled trap. The BrF was added portionwise, and the temperature of the reactants adjusted between 25 and 50 C so that the reaction progressed at a rapid but controllable rate. When the reaction was complete, water was cautiously added to decompose any BrF which remained. The reaction product was freed of hydrogen fluoride and bromine by successive washings with water,sodiurn sulfite solution and water. The washed product was dried by freezing out water at 20 C. The dried product weighed 541 grams and was 98.3 percent fluoromethyl 1,1,l,3,3,3- hexafluoro-Z-propyl methyl ether and 1.7 percent the starting methyl ether by gas-liquid chromatography. In addition, the trap contained 92 grams of about a 1:1 mixture of these fluoromethyl and methyl ethers. Fractional distillation of the 541 grams of product gave purified fluoromethyl 1 ,1 ,1,3,3,3-hexafluoro-2-propyl ether: 343 grams of better than 99.9 percent purity, b 58.1 58.2 C, d 23 1.505; and 95 grams ofbetter than 99.0 percent purity.

EXAMPLE 6 Fluoromethyl 1 l l ,3,3 ,3-Hexafluoro-2-propyl Ether 1 ,1 l ,3,3,3-hexafluoro-2-propanol, paraformaldehyde and anhydrous hydrogen fluoride in a, respective, 1:2:4 molar ratio were stirred at about 9 C. In about 30 minutes, the homogeneous mixture began to deposit a crystalline product. After about 2 hours, this product was collected by filtration, washed with water, and then allowed to dry overnight in room air, m.p. 52.5 C, yield 52 percent by weight based on hexafluoro-2-propanol. After one recrystallization from carbon tetrachloride, this compound had m.p. 54.6 C and micro b.p. 154.5 C at 753 torr. The proton NMR spectrum of this compound in CCl, (0.10 g./ml.)

showed a singlet (6 =4.27 ppm) and a septet (6 3.60 ppm, J 6H2) in an area ratio of 2:1. The chemical shifts (6) are given relative to internal tetramethyl silane. A tentative structure for this compound is [(CF CHOCH O. The latter compound (m.p. 54.6 C) and anhydrous hydrogen fluoride in a 1:1.33 weight ratio were heated in a steel autoclave for two hours at -1 10 C, then for 4 hours at C and then cooled. After removal of hydrogen fluoride, the remaining liquid, water-immiscible product (40 percent by weight based on the compound m.p. 54.6 C) was found by proton nuclear magnetic and gasliquid chromatographic analyses to be about 90 percent fluoromethyl 1,1,1,3,3,3-hexafluoro-2-propyl ether.

EXAMPLE 7 The fluoromethyl l 1 1 ,3,3 ,3-hexafluoro-2-propyl ether of this invention was shown to have useful anesthetic properties in mice essentially according to the procedure described by Robbins, J. Pharmacol. Exptl. Therap., Vol. 86, pages 197-204 (1946). The five minute median anesthetic concentration, AC and the 5 minute median lethal concentration, LC were determined by a log-probit plot of the data as described by Miller and Tainter, Proc. Soc. Exptl. Biol. Med., Vol. 57, pages 261-264 (1944). The number of test mice used was 30 for each of the AC and LC concentrations. Fluoromethyl l 1 1 ,3 ,3,3-hexafluoro- 2-propyl ether was found to have an AC of 1.42 volume percent and an LC of 8.38 volume percent, or an anesthetic margin of safety (LC /AC of 5.9 in mice. Identical tests with several anesthetics in general use gave the following results:

halothane, LC /AC 274/078 3 .5;

diethyl ether, LC lAC 136/383 3.5;

fluroxene, LC /AC =11.6/3.5 =33;

methoxyflurane, LC /AC 2.5 2/0.56 4.5.

EXAMPLE 8 In order to demonstrate the unexpected and unobvious outstanding anesthetic properties of the fluoromethyl l 1 1 ,3 ,3 ,3-hexafluoro-2-propyl ether compared to the corresponding properties of various of its isomers and analagous compounds, the following tests were conducted:

Dogs and rats anesthetized 3 hours daily, 5 days per week for 2 weeks, with fluoromethyl l,l,l,3,3,3-hexafluoro-2-propyl ether in oxygen showed no signs of toxicity. Anesthesia proceeded smoothly and rapidly, the anesthetic state was unmarked by convulsive movements or electroencephalographic abnormalities, and recovery occurred within two minutes. On the other hand, chloromethyl 1 1 1 ,3,3 ,3-hexafluoro2-propyl ether produced severe toxic signs and death in rats and dogs anesthetized 3 hours daily on 5 consecutive days. In mice, recovery time was undesirably prolonged to 18 to 20 minutes following only 10 minutes of anesthesia with CF (CF Cl)CHOCH Cl and in mice anesthetized with (CF CHOCHFCl,' opisthotonus was observed during induction. In dogs, (CF CHOCHF produced anesthesia marked by convulsive movements and electro-encephalographic abnormalities. The compound (CI-IF CFOCI-IF caused loss of righting reflex in mice but produced only hypnosis and clonic convulsive activity with little analgesia in dogs.

EXAMPLE 9 In still another comparison between fluoromethyl l,l,l,3,3,3-hexafluoro-2-propyl ether and several close analogs administered to dogs via the inhalation route, the following results were obtained:

ANlCS'llllI'llU COMPARISON IN DOGS luiluetiou Miiluti'iuiiu-o Number of Concentration, 'liuii, (itllllfllllil'illillllI; Recovery time, Compound lest (logs vol. percent minutes vol. percent iiiluutes Results lll CII F1O-C-C I"; 8 (3-8 5 445 5-25 No significant side eilects after single I or repeated exposures. C F3 CH2C1O-CC F Cl 3 3.1 20 0.2-0.5 No recovery. Spontaneous leg movements during Cardiac anesthesia, severe respiratory and F3 failure. cardiac depression.

H CHFCl-O( )*C F3 1 dog, 4 5 2-3 -30 EEG seizure discharges and eonexposures. vulsive movements during zines- C F3 tliesia. i CIIF:-O-CCF; .3 H 3 15 0.5-1.0 No rec0veries Spontaneous cardiac arrhythmias, high amplitude EEG spiking and CFzCl convulsive movements during anestliesia.

*Aiiestliesia maintained for 2-3 li0urs in each dog.

EXAMPLE 10 methyl hexafluoro-Z-propyl ether was 6.0 and its LFLO /AC ratio was 2.70. The flammability of gaseous mixtures of fluoromethyl l,1,1,3,3,3-hexafluoro-2-propy ether Otfher examples g g g fif and oxygen were determined at room temperature and Hons O t Orlagomg examp es can e evlse y e atrnos heric ressureb visualization of the downward persc-m sk-med m the an after reqdmg e foregomg p ti fl l boa] h specification and the appended claims without departtheoflhe bottle g flushed with p g a known q a y further examples, modifications and adaptations are included within the sco e of the invention. of the liquid anesthetic was added rapidly, and the bot- What is claimed He i 3 gg g z i g g figagzisgz 40 1. The method of inducing anesthesia in animals 3i g; i 3: f 2 unifomclll mixed with comprising administering by inhalation to an animal an ox en 'l he stc ei' was then removed an d immediate effecnve amount for mducmg anesthesla of i Zi bu min sa was inserted in the bottle 1 5 to 2 0 flummelhyl TP s. i es 610%, e b0 6 o m 2. An inhalant anesthetic composition comprising e lower i l amm alail i t y limit in oxygen, LFLO of the Compound of clalm 1 gasequs qdmlxture the gaseous anesthetic was defined as the concentray In Q P sllltable' F maintain anesthesia and tion by volume percent of the anesthetic in the gaseous Support resplratlon f mixture at which downward flame propagation was ob- T 9 of anethe51a @mmals served comprising administering by inhalation to an animal an The concentration by volume percent of the gaseous FP amolmt for Inducing anestmsla 0f the anesthetic in oxygen was calculated by well-known Posmon Ofclalm computation means employing the known volumes,

' UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. .3, 683, 092 Dated August 8, 1972 Inventor(s) Bernard M. Regan and John C. Longstreet It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the specification, col. '7, in the table under Example 9, the first listed structural formula should appearas follows:

CH F-OC-CF Signed and sealed this 6th day of August 197A (SEAL) Attest:

MCCOY GIBSON, JR. I c. MARSHALL DANN Attesting Officer Commissioner of Patents 

2. An inhalant anesthetic composition comprising the compound of claim 1 in gaseous admixture with oxygen in amounts suitable to maintain anesthesia and support respiration in an animal.
 3. The method of inducing anesthesia in animals comprising administering by inhalation to an animal an effective amount for inducing anesthesia of the composition of claim
 2. 